The present invention relates generally to swashplate-controlled hydraulic units which convert rotational power to fluid power and vice versa. The present invention relates to axial piston, variable displacement hydraulic pumps. More particularly, this invention relates to an improved unitary housing for axial piston hydraulic units having a plurality of rotary groups.
Various configurations of multiple pumps are known in the art of hydraulics. Two, three, or even more pumps have been coupled together so as to be driven by a single source of rotary power. One configuration known as a tandem pump or double pump is quite common.
A typical conventional tandem pump comprises a front pump having a housing and a shaft mounted to the source of rotary power and a rear pump having its own housing and shaft mounted to the rear of the front pump. The shafts of the front and rear pump are drivingly connected to each other by a coupling positioned between them. Each pump in the tandem pump combination has its own rotating group and swashplate. The rotating group includes a cylinder block and a plurality of axially reciprocable pistons mounted therein.
Each pump in the tandem also includes a valve plate for controlling the timing and direction of the fluid flow of the respective pump. The valve plate mates with the end of the cylinder block that is opposite from the swashplate. Bi-directional valve plates are known to improve the flexibility of hydraulic units by allowing the unit to be driven in either direction by a source of rotary power, but performance and efficiency have been lacking or compromised with these bi-directional valve plates. Therefore, existing tandem hydraulic units are usually built with valve plates of a specific porting configuration so as to correspond with the direction that the source of rotary power rotates. The surfaces of the cylinder blocks that mate with the valve plates generally face in the same direction in conventional tandem pumps. Therefore, each pump in the tandem must use a valve plate that has the same rotational configuration as the valve plate of the other pump and the source of rotary power.
Because of the uni-directional nature of most conventional hydraulic pumps, manufacturers and distributors can often have difficulty meeting customer demand for a unit of a particular rotation. If the hydraulic pump and the customer's source of rotary power are of opposite rotations, either a different hydraulic unit must be built from scratch or obtained otherwise. It is known in the art that it is sometimes quicker to partially disassemble and then convert a unit of incorrect rotation to a unit of the desired rotation by changing the valve plate. In fact, both valve plates in a tandem must be changed to complete the conversion. The known configurations of tandem pumps make it difficult for manufacturers and distributors to provide efficient units of the desired rotation without long delays or high inventory carrying costs.
Existing tandem pumps are also difficult to convert to a different rotation because the valve plate is located at the bottom of a stack of components such that it can only be removed through an opening at the end of the housing. Numerous other components must first be removed to expose the valve plate. The difficulty is compounded when the tandem pump has already been installed in the vehicle. The tandem pump may have to be disconnected from the source of rotary power before conversion can commence. If an auxiliary gear pump or the like is mounted to the rear pump, it may also have to be removed prior to attempting the conversion.
The pressure generated by the axial pistons of the hydraulic unit can reach several thousand pounds per square inch. This high pressure translates into large axial forces during the operation of the hydraulic unit. Conventional tandem pumps typically comprise two pump housings joined at a seam that is transverse to the direction of these major axial hydraulic forces. As a result, the large axial forces tend to separate the housings at their seam or joint and let fluid leak out. Various sealing means such as o-rings, seals, and gaskets have been tried to seal this joint. The long term reliability of such sealed joints remains a concern.
In order to restrain the housings against the separation forces caused by the axial hydraulic loads, various fastening systems have been tried along the seam or joint between them. Such fastening systems consume a great deal of space, and thereby require a housing which is larger than necessary. Since the size of the housing is a major factor in determining the overall size of the hydraulic unit, a larger housing means a larger hydraulic unit. Larger hydraulic units typically weigh more, require more materials, cost more and consume more space when installed.
Logically, the length of multiple pumps, tandem pumps included, can be quite long. Furthermore, auxiliary pumps, such as gear pumps, gerotor pumps, crescent pumps, vane pumps and the like are often mounted on an SAE pad at the back of the rear pump. As a result of this extended length and weight, auxiliary support brackets are sometimes required to relieve the stress and deflection which would otherwise occur at the seam (s) of the housings.
Therefore, a principle objective of the present invention is the provision of an improved housing for multiple hydraulic units.
A further object of this invention is to provide a housing for a multiple hydraulic unit that is more reliable and flexible.
A further objective of this invention is to provide a unitary hydraulic housing which eliminates seams or joints transverse to the direction of the major hydraulic separating forces.
A further objective of this invention is the provision of a multiple hydraulic unit assembly which can be adapted to the rotation of a source of rotary power without a major teardown of the unit.
A further objective of this invention is the provision of a tandem hydraulic unit assembly having identical mounting flanges at both ends of its housing and back-to-back cylinder blocks such that the rotation of the tandem can be changed by spinning or flipping the unit end-for-end.
A further objective of this invention is the provision of a unitary housing for a multiple hydraulic unit having a transverse aperture for the insertion and withdrawal of a rotating group and valve plate.
A further objective of this invention is the provision of a unitary housing for a multiple hydraulic unit that reduces the need for an auxiliary supporting bracket to be attached to the hydraulic unit in order to relieve stress and reduce deflection.
These and other objectives will be apparent to those skilled in the art.